Need Help with an Air Flow Problem?

We are having trouble calculating a required ft^3 per minute air flow for a particular vessel which was constructed to measure the accuracy of a vacuum machine.
Our vessel is a steel cylindrical drum 1mm thick with a diameter of 22.5" and a height of 34.5". It has 50 holes around the lower perimeter measuring 13 mm in diameter. What is the air flow rate if we pull a vacuum of 1" of H20 at a temp of 70 deg. F and Relative Humidity of 26%. Can anyone help us out?